With the progress in colorization and digitization of an electrophotographic copier and printer, the improvement of the image quality of electrophotographic has hitherto been discussed. In particular, in an electrophotographic full color copier and printer, digitization of input/output of images has been advanced for obtaining an image of high image quality, and an inputting method of images, a processing method of inputted images, a developing method, a transferring method, a fixing method, etc., have been largely improved. Further, a developer and an image-forming material of a photoreceptor have been improved correspondingly to high digital precision and color recording of highly developed color.
However, since toners having a particle size of from several micrometers to several ten micrometers are used in an electrophotographic full color copier and printer, if a plain paper or a coated paper is used as an image support, toners expand slightly above the level irregularly between high density areas and low density areas. As a result, the unevenness of the gloss of the surface is generated and there arises a problem such that the image quality thus obtained is inferior to those of a photographic image and a printed image.
In order to improve such a problem, JP-A-63-92965 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes a technique which comprises providing, on an image support, a transparent resin layer having a thickness thicker than a certain value, the softening point of a transparent resin used in the transparent resin layer being lower than that of the toner, and embeding a toner image in the transparent resin layer using a roller type fixing apparatus.
Moreover, JP-A-5-127413 discloses a method, for the same purpose as the above method, which comprises overlaying a toner image on an image support having a transparent resin layer comprising a crosslinked resin which has a glass transition temperature within a specific range and is soluble in a tetrahydrofuran, and embeding the toner image into the transparent resin layer using a belt type fixing apparatus.
Still further, JP-A-5-216322 and JP-A-6-11982 disclose a method similar to the latter method, which comprises providing a transparent resin layer comprising a thermoplastic resin having a certain thickness on an image support, transferring and adhering a toner thereon, and embeding the toner image into the transparent resin layer using a belt type fixing apparatus.
However, in JP-A-63-92965, since the softening point of the transparent resin is lower than that of the toner, the transparent resin becomes soft faster than the toner and becomes liable to flow upon application of heat and pressure using a fixing apparatus. As a result, troubles arise such that the image area is dimpled like a shell pattern to vanish the surface gloss, that the transparent resin layer is taken away by the fixing apparatus, thereby the image is lost, and that the transfer sheet per se adheres to the fixing apparatus (hereinafter this phenomenon is called an offset phenomenon). Further, since the transparent resin is soft and the layer thickness is thick, the toner is liable to permeate the layer in a granular state and colors are not developed sufficiently or the toner does not mix with each other. Therefore, the original colors cannot be reproduced faithfully. That is, color reproducibility is reduced.
There are disclosed in JP-A-5-127413, JP-A-5-216322 and JP-A-6-11982 that according to these methods described therein the above-described offset phenomenon hardly occurs due to the employment of a belt type fixing apparatus. However, since the thickness of the transparent resin layer is thick, e.g., from 20 to 200 .mu.m, the compatibility with the toner is not taken into consideration, the toner is liable to get into the image-receiving layer as it is without sufficiently melting. As a result, particularly in the secondary color part, there is a possibility that sufficient color mixture does not occur and reproduced colors differ from the original colors. Thus, color reproducibility is deteriorated.